Haemoptysis is the coughing of blood from a source below the glottis.  It can range from a small amount of blood-streaked sputum to massive bleeding with life-threatening consequences due to airway obstruction and haemodynamic instability.
It is a common condition, accounting for 15% of all pulmonary consultations, and is the second most common indication for flexible bronchoscopy.   The rate of bleeding has been described as the most important factor determining mortality. 
The initial diagnostic assessment should aim to differentiate between haematemesis (i.e., the vomiting of blood), pseudohaemoptysis (i.e., the coughing of blood from a source other than the lower respiratory tract), and haemoptysis. Pseudohaemoptysis can occur when: 
Haematemesis is aspirated into the lungs
Bleeding from the upper airway or the mouth stimulates a cough reflex
Material is expectorated that looks like blood but is not (e.g., Serratia marcescens infection).
Characteristically, haemoptysis tends to be indicated by bright red, frothy sputum that is alkaline and with an oxygen saturation (SaO2) similar to peripheral arterial saturation. Blood from extrapulmonary sources tends to be darker, may have admixed food particles, is acidic, and has an oxygen saturation similar to that found in venous blood.   The exception is when brisk bleeding in the gastrointestinal tract overcomes the acidic environment of the stomach, or when arterial bleeding occurs in an extrapulmonary site. Examining the oral and nasal cavities can provide important clues to the source of the bleeding (e.g., telangiectasia in the mouth or nose, etc).
Various definitions of massive haemoptysis exist. A common definition is the expectoration of blood from a source below the glottis exceeding 600 mL of blood over a 24-hour period or 150 mL of blood (which may flood the lung deadspace) over a 1-hour period. Massive haemoptysis is a medical emergency and should be addressed immediately. Initial priorities are stabilisation of the patient and protection of the non-bleeding lung.
Haemoptysis has numerous possible causes, including tracheobronchial, pulmonary parenchymal, and pulmonary vascular diseases. In the primary care setting, major causes are acute and chronic bronchitis, tuberculosis, lung cancer, pneumonia, and bronchiectasis.
Clinical, radiological, and pathological evidence has demonstrated that the bronchial or systemic circulation is responsible for most cases of haemoptysis.  However, the pulmonary circulation has also been implicated, as is the case in catheter-induced pulmonary artery rupture, vasculitis, pulmonary artery aneurysms due to collagen vascular disease, or hereditary haemorrhagic telangiectasia.  
Co-Director, Interventional Pulmonology
Chief, Complex Chest Disease Center
Massachusetts General Hospital
Harvard Medical School
EF is an author of a reference cited in this monograph.
Dr Erik Folch would like to gratefully acknowledge Professor James K. Stoller, a previous contributor of this topic. JKS is an author of a number of references cited in this monograph.
Box Hill Hospital and Monash University
FT declares that he has no competing interests.
Interventional Radiologist and Pulmonologist
Full Professor and Chief of Interventional Radiology
University of Zaragoza
MAdG has been reimbursed by Cook Medical and Abbott Vascular for attending several conferences; by Cook Medical and UCB Pharma for speaking; by Cook Medical and St Jude Medical for running educational programs.
Division of Pulmonary & Critical Care Medicine
US Department of Veterans Affairs
Palo Alto Health Care System
Clinical Assistant Professor of Medicine
Stanford University School of Medicine
HSP declares that he has no competing interests.
Medical Intensive Care Unit
West Los Angeles VA Healthcare Center
GWSH declares that he has no competing interests.
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